1// Copyright (c) 2009 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "kern.h"
6
7// kern - Kerning
8// http://www.microsoft.com/opentype/otspec/kern.htm
9
10#define DROP_THIS_TABLE \
11  do { delete file->kern; file->kern = 0; } while (0)
12
13namespace ots {
14
15bool ots_kern_parse(OpenTypeFile *file, const uint8_t *data, size_t length) {
16  Buffer table(data, length);
17
18  OpenTypeKERN *kern = new OpenTypeKERN;
19  file->kern = kern;
20
21  uint16_t num_tables = 0;
22  if (!table.ReadU16(&kern->version) ||
23      !table.ReadU16(&num_tables)) {
24    return OTS_FAILURE();
25  }
26
27  if (kern->version > 0) {
28    DROP_THIS_TABLE;
29    return true;
30  }
31
32  if (num_tables == 0) {
33    OTS_WARNING("num_tables is zero");
34    DROP_THIS_TABLE;
35    return true;
36  }
37
38  kern->subtables.reserve(num_tables);
39  for (unsigned i = 0; i < num_tables; ++i) {
40    OpenTypeKERNFormat0 subtable;
41    uint16_t sub_length = 0;
42
43    if (!table.ReadU16(&subtable.version) ||
44        !table.ReadU16(&sub_length)) {
45      return OTS_FAILURE();
46    }
47
48    if (subtable.version > 0) {
49      OTS_WARNING("Bad subtable version: %d", subtable.version);
50      continue;
51    }
52
53    const size_t current_offset = table.offset();
54    if (current_offset - 4 + sub_length > length) {
55      return OTS_FAILURE();
56    }
57
58    if (!table.ReadU16(&subtable.coverage)) {
59      return OTS_FAILURE();
60    }
61
62    if (!(subtable.coverage & 0x1)) {
63      OTS_WARNING(
64          "We don't support vertical data as the renderer doesn't support it.");
65      continue;
66    }
67    if (subtable.coverage & 0xF0) {
68      OTS_WARNING("Reserved fields should zero-filled.");
69      DROP_THIS_TABLE;
70      return true;
71    }
72    const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
73    if (format != 0) {
74      OTS_WARNING("Format %d is not supported.", format);
75      continue;
76    }
77
78    // Parse the format 0 field.
79    uint16_t num_pairs = 0;
80    if (!table.ReadU16(&num_pairs) ||
81        !table.ReadU16(&subtable.search_range) ||
82        !table.ReadU16(&subtable.entry_selector) ||
83        !table.ReadU16(&subtable.range_shift)) {
84      return OTS_FAILURE();
85    }
86
87    if (!num_pairs) {
88      OTS_WARNING("Zero length subtable is found.");
89      DROP_THIS_TABLE;
90      return true;
91    }
92
93    // Sanity checks for search_range, entry_selector, and range_shift. See the
94    // comment in ots.cc for details.
95    const size_t kFormat0PairSize = 6;  // left, right, and value. 2 bytes each.
96    if (num_pairs > (65536 / kFormat0PairSize)) {
97      // Some fonts (e.g. calibri.ttf, pykes_peak_zero.ttf) have pairs >= 10923.
98      OTS_WARNING("Too large subtable.");
99      DROP_THIS_TABLE;
100      return true;
101    }
102    unsigned max_pow2 = 0;
103    while (1u << (max_pow2 + 1) <= num_pairs) {
104      ++max_pow2;
105    }
106    const uint16_t expected_search_range = (1u << max_pow2) * kFormat0PairSize;
107    if (subtable.search_range != expected_search_range) {
108      OTS_WARNING("bad search range");
109      subtable.search_range = expected_search_range;
110    }
111    if (subtable.entry_selector != max_pow2) {
112      return OTS_FAILURE();
113    }
114    const uint32_t expected_range_shift
115        = kFormat0PairSize * num_pairs - subtable.search_range;
116    if (subtable.range_shift != expected_range_shift) {
117      OTS_WARNING("bad range shift");
118      subtable.range_shift = expected_range_shift;
119    }
120
121    // Read kerning pairs.
122    subtable.pairs.reserve(num_pairs);
123    uint32_t last_pair = 0;
124    for (unsigned j = 0; j < num_pairs; ++j) {
125      OpenTypeKERNFormat0Pair kerning_pair;
126      if (!table.ReadU16(&kerning_pair.left) ||
127          !table.ReadU16(&kerning_pair.right) ||
128          !table.ReadS16(&kerning_pair.value)) {
129        return OTS_FAILURE();
130      }
131      const uint32_t current_pair
132          = (kerning_pair.left << 16) + kerning_pair.right;
133      if (j != 0 && current_pair <= last_pair) {
134        OTS_WARNING("Kerning pairs are not sorted.");
135        // Many free fonts don't follow this rule, so we don't call OTS_FAILURE
136        // in order to support these fonts.
137        DROP_THIS_TABLE;
138        return true;
139      }
140      last_pair = current_pair;
141      subtable.pairs.push_back(kerning_pair);
142    }
143
144    kern->subtables.push_back(subtable);
145  }
146
147  if (!kern->subtables.size()) {
148    OTS_WARNING("All subtables are removed.");
149    DROP_THIS_TABLE;
150    return true;
151  }
152
153  return true;
154}
155
156bool ots_kern_should_serialise(OpenTypeFile *file) {
157  if (!file->glyf) return false;  // this table is not for CFF fonts.
158  return file->kern != NULL;
159}
160
161bool ots_kern_serialise(OTSStream *out, OpenTypeFile *file) {
162  const OpenTypeKERN *kern = file->kern;
163
164  if (!out->WriteU16(kern->version) ||
165      !out->WriteU16(kern->subtables.size())) {
166    return OTS_FAILURE();
167  }
168
169  for (unsigned i = 0; i < kern->subtables.size(); ++i) {
170    const uint16_t length = 14 + (6 * kern->subtables[i].pairs.size());
171    if (!out->WriteU16(kern->subtables[i].version) ||
172        !out->WriteU16(length) ||
173        !out->WriteU16(kern->subtables[i].coverage) ||
174        !out->WriteU16(kern->subtables[i].pairs.size()) ||
175        !out->WriteU16(kern->subtables[i].search_range) ||
176        !out->WriteU16(kern->subtables[i].entry_selector) ||
177        !out->WriteU16(kern->subtables[i].range_shift)) {
178      return OTS_FAILURE();
179    }
180    for (unsigned j = 0; j < kern->subtables[i].pairs.size(); ++j) {
181      if (!out->WriteU16(kern->subtables[i].pairs[j].left) ||
182          !out->WriteU16(kern->subtables[i].pairs[j].right) ||
183          !out->WriteS16(kern->subtables[i].pairs[j].value)) {
184        return OTS_FAILURE();
185      }
186    }
187  }
188
189  return true;
190}
191
192void ots_kern_free(OpenTypeFile *file) {
193  delete file->kern;
194}
195
196}  // namespace ots
197